Wintertime irruption

A goal in birding common to most birders is the hope of one day seeing a rare bird. At first, identifying any bird is exciting, but as you learn more about your local species, there’s often the desire to see something others have not.

Most exciting is the finding of a species that is only found in another part of the country, or is even from another continent. In the Northwest we get a few wanderers from Asia that have arrived via Alaska and have worked their way down the coast.

Not many years back a Siberian accentor, a pipitlike bird from, as you might have guessed, Siberia was found wintering in Idaho. Other than that sighting, accentors have only been seen rarely in Alaska and once in Washington. You can imagine the reaction of the birder who first found that one.

Another winter an Eastern species, a pine warbler, was seen at a feeder for a week or so in Moscow. The owners of the feeder became instant celebrities in the bird world and were inundated by visitors, including me, willing to drive long distances in bad weather to see this oddity.

How such individuals get so far off course, and what finally becomes of them is a source of lively debate. The warbler should have been wintering in Florida and was not well equipped to survive a North Idaho winter. Chances are that its genes never made it into the pine warbler gene pool and that it ultimately became some predator’s dinner.

Other types of rarities that birders watch for are those species that are usually not here but can be expected on an occasional basis. Snowy owls are one of the more common examples, and last year at about this time we had one on the Rathdrum Prairie. The last Kootenai County snowy owl had been seen four years previous.

Many winters we also see common redpolls, a finch that breeds in the Arctic. In 2002, common redpolls were especially abundant in our area, and its close, but extremely rare relative, the hoary redpoll, was seen in North Idaho and northern Washington in unprecedented numbers.

An invasion of numerous members of a species such as the snowy owl or the common redpoll is called an irruption. An eruption is what Mount St. Helens does. An eruption could cause an irruption, but they are not the same thing. I wonder if it’s like emigration and immigration. In the Arctic do birders say that the snowy owls are erupting as they leave? In any event, an irruption is when a species of northern breeders makes an unusual migration into more southern areas for various and often unknown reasons.

This winter we are experiencing an irruption of another sort that has North Idaho birders dancing in the snow. This species is our largest finch, the pine grosbeak.

Pine grosbeaks breed in Kootenai County, but are seldom seen by county birders because they nest at high elevations that are relatively difficult to get to and where birders are less likely to be looking. During extensive birding in the county over the past six years, the pine grosbeak has not even been on the list of observed species half of those years.

Pine grosbeaks favor open areas near timberline in forests of spruce and subalpine fir for their summer habitat, and they seldom wander far from these areas in winter. As an aside, the pine grosbeaks in our locale, at least, don’t really care for pines. I hope that they are not offended by the name.

I saw my first pine grosbeak while wading hip-deep in powder snow on Bernard Peak, overlooking Farragut State Park. Most of my other pine grosbeak sightings have been from the chairlift at Schweitzer ski resort. The only low-elevation grosbeaks on my list were in a small flock of females on Rathdrum Mountain in 2001.

This year, however, pine grosbeaks are all over the place. In just the past few weeks, I have seen reports of low-elevation birds from Priest River, Hayden, Coeur d’Alene, Moscow (wow!), and from both Spokane and Lincoln Counties in Washington. None of these areas is typical pine grosbeak habitat, by any means. We are truly in the midst of a grosbeak irruption.

However, as I indicated earlier, most irruptions are latitudinal. Snowy owls and redpolls come to us from the Arctic. Pine grosbeaks are coming to us from our own mountains. They are irrupting altitudinally.

Pine grosbeaks are found all across the northern parts of North America and Eurasia, but are especially unique in western North America. Here they breed in the Rocky Mountains as far south as Arizona and New Mexico. In the East they are not usually found in the United States except in winter.

In the West, pine grosbeaks can be found in isolated populations in the Sierra Nevada Mountains of California, on a British Columbia island, and along the coast of Alaska, and they have unique appearances in each place. In the East all pine grosbeaks are pretty much alike. Even our Rocky Mountain population, called the interior West form, looks different from the eastern birds.

Pine grosbeaks are large by finch standards at eight birds to the pound, and are robin-sized, long-tailed and stubby-billed. As with many other finches, males and females are colored differently; they are sexually dimorphic. Our male Rocky Mountain grosbeaks are the least brightly colored of all races, but they are still showy in their red head, rump and breast feathers. Similar to crossbills, female pine grosbeaks are marked with greenish-yellow where males are red. Immature males are indistinguishable, in most cases, from females, but a few in our area will actually be russet-colored – sort of half way between the colors of the adult plumages.

Grosbeak irruptions are apparently triggered by shortages of food in their normal areas. Pine grosbeaks are among the most winter-hardy of birds, often remaining above the Arctic Circle year-round. So when they come down to our level, they must be hungry. In their usual habitat they will spend the winter nipping the buds from fir and alder, and mashing the seeds from any berry-like fruits they can find. In town areas, they seek out the remains of neglected apple orchards and the orange berries on ornamental mountain ash trees.

Whereas the robins and waxwings that also favor mountain ash berries consume the whole fruit, pine grosbeaks mash the fruit, extract the seeds, spit out and drop the fruit, then crush and swallow the seeds. Robins and waxwings will also strip a tree clean of fruit in hours, but a grosbeak flock will spend days retrieving every last berry before moving on.

I have no idea what’s going on up in those mountains around us that is driving the pine grosbeaks our way, but it’s way too cold and snowy for me to go up there looking. I’m satisfied with my single hip-deep-in-snow sighting. This year I’m glad to let the grosbeaks irrupt my way. There’s no telling when they’ll be here again, so enjoy our Kootenai County pine grosbeaks now, before they erupt back.